This invention relates to an information recording apparatus for recording information by irradiating an information recording medium with an energy beam.
As apparatuses for recording digital signals such as signals obtained by frequency-modulating analogue signals of image, sound, etc., data of electronic computers, facsimile signals, digital audio signals, etc. in real time, there are used apparatuses for recording information by irradiating an information recording medium with an energy beam such as a laser beam, electron beam, etc.
Heretofore, as apparatuses for recording information by irradiating the information recording medium with a laser light beam, there are known apparatuses, in which various changes such as deformation, phase change, chemical change, change in the magnetic field, etc. are produced in the information recording medium, depending on the waveform of the laser light pulse. Among them those using deformation are disclosed e.g. in U.S. Pat. No. 4,238,803 and those using phase change are described in U.S. Pat. No. 3,530,441.
However, in such prior art information recording apparatuses, in the case where pulses of an energy beam, as indicated in FIG. 1(a), are projected thereon, the waveform of reproduced signals is deformed as indicated in FIG. 1(b) and it is not possible to specify the recorded position with a high precision. For this reason the reproduced signal is differentiated so as to transform it into a signal as indicated in FIG. 1(c) and the recorded position is defined as the position, where the signal level is 0. Therefore the prior art information recording apparatus required a differential circuit, which gave rise to problems that the signal to noise ratio decreased and that the apparatus was too expensive. Further there was another problem that tracking off-set or focusing off-set was easily produced, because the mean reflectivity on the recording track was varied by the fact that information was recorded there.